I would do the alt bypass as suggested running the power directly to the start relay then run a bank of relays from there like all the new cars do to send power directly to the fans etc that way none of the heavy load has to go through the fire wall at all . The firewall connectors are not designed to carry high loads . You probably need a high load wire say 6 - 8 gauge to the start relay & a low load signal wire to the alt to tell the built in reg when to charge , the blue wire at the voltage reg should work for this .
I did this on a RR , I had a custom 110 amp alt built , & pirated a relay center from a car in the wreckers , we had 2 fuel pumps , electric water pump , 3 electric fans, & the EFI computer to run , 60 amps was not enough .